package com.iluwatar.doublechecked.locking;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
 * 
 * Double Checked Locking is a concurrency design pattern used to reduce the overhead 
 * of acquiring a lock by first testing the locking criterion (the "lock hint") without 
 * actually acquiring the lock. Only if the locking criterion check indicates that 
 * locking is required does the actual locking logic proceed.
 * <p>
 * In {@link Inventory} we store the items with a given size. However, we do not store
 * more items than the inventory size. To address concurrent access problems we
 * use double checked locking to add item to inventory. In this method, the
 * thread which gets the lock first adds the item.
 * 
 */
public class App {

	/**
	 * Program entry point
	 * @param args command line args
	 */
	public static void main(String[] args) {
		final Inventory inventory = new Inventory(1000);
		ExecutorService executorService = Executors.newFixedThreadPool(3);
		for (int i = 0; i < 3; i++) {
			executorService.execute(() -> {
                while (inventory.addItem(new Item()))
                    ;
            });
		}

		executorService.shutdown();
		try {
			executorService.awaitTermination(5, TimeUnit.SECONDS);
		} catch (InterruptedException e) {
			System.out.println("Error waiting for ExecutorService shutdown");
		}
	}
}
